1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of a recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head section having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head section includes a main pole that produces a magnetic field in a direction perpendicular to the plane of a recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces a recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head section of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of a recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
Here, the side of positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the backward side in the direction of travel of a recording medium relative to the slider. The trailing side is the forward side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over a recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For achieving higher recording density, it is necessary to prevent adjacent track erasure.
Providing a write shield near the main pole is effective for preventing adjacent track erasure induced by the skew mentioned above and increasing the recording density. The write shield has an end face located in the medium facing surface. For example, U.S. Patent Application Publication No. 2009/0015965 A1 discloses a magnetic head including a return yoke that forms a magnetic path in conjunction with the main pole. The return yoke includes a return yoke tip having an end face that is located in the medium facing surface and spaced from an end face of the main pole by a predetermined distance. The return yoke tip functions as a write shield.
In a magnetic head having a write shield, there are typically provided one or more return path sections for connecting the write shield and part of the main pole away from the medium facing surface to each other. The write shield and the one or more return path sections have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of a recording medium, so as to prevent the magnetic flux from reaching the recording medium. The write shield and the one or more return path sections also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. Thus, the magnetic head having the write shield makes it possible to prevent the occurrence of adjacent track erasure and achieves a further improvement in recording density.
The position of an end of a record bit to be recorded on a recording medium depends on the position of the trailing-side end of the end face of the main pole located in the medium facing surface. To define the position of the end of the record bit with high accuracy, it is therefore effective to provide the write shield with an end face including an end face portion located on the trailing side relative to the end face of the main pole.
In addition, as the frequency of a recording signal is increased in order to increase the recording density, the magnetic head is required to be improved in the rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement in the magnetic head having a write shield, it is particularly effective to provide a return path section that is located on the trailing side relative to the main pole and to reduce the length of the return path section, in addition to forming the end face of the write shield to include an end face portion located on the trailing side relative to the end face of the main pole.
U.S. Patent Application Publication No. 2009/0015965 A1 discloses a technology for reducing the yoke length which is related to the length of the return path section located on the trailing side relative to the main pole. Specifically, the technology provides a coil encompassing the main pole in a solenoid structure. The coil includes a lower wire portion passing through the lower portion of the main pole, an upper wire portion passing through the upper portion of the main pole, and a connection portion electrically connecting the lower wire portion and the upper wire portion. The upper wire portion includes an upper wire layer having a stack of at least two layers.
The magnetic head disclosed in U.S. Patent Application Publication No. 2009/0015965 A1 has the following problems, however. In this magnetic head, the upper wire portion includes a first upper wire layer which is relatively closer to the main pole and a second upper wire layer which is relatively farther from the main pole. The return yoke includes a portion that is located farther from the medium facing surface than is the upper wire portion. The bottom surface of this portion is in contact with the top surface of a sub-yoke provided on the main pole. The aforementioned portion of the return yoke will hereinafter be referred to as the back gap portion. The distance from the medium facing surface to an arbitrary point on an end of the back gap portion facing toward the medium facing surface increases stepwise with decreasing distance from the arbitrary point to the main pole. Such a shape of the back gap portion causes the direction of a magnetic flux flowing from the back gap portion toward the sub-yoke to change at a great angle of 90° or more in the vicinity of the interface between the back gap portion and the sub-yoke. This may induce leakage of magnetic flux in the vicinity of the interface between the back gap portion and the sub-yoke, and thereby hinder the main pole from producing a write magnetic field of sufficient magnitude.
As such, it has conventionally been difficult to allow the main pole to produce a write magnetic field of sufficient magnitude while reducing the length of a magnetic path that passes through a return path section and the main pole, the return path section being located forward in the direction of travel of a recording medium (i.e., located on the trailing side) relative to the main pole.